Diaper that includes weldable fastener devices

ABSTRACT

An absorbent article, such as a diaper, a pants-type diaper, an incontinence protector or a pants-like sanitary napkin, having a front part, a rear part and an intermediate central part. The article includes an absorbent body enclosed between an inner, liquid-permeable sheet and a liquid-impermeable outer sheet, and fastener devices for releasably connecting side-portions of the front and rear parts. The fastener devices are made of a renewable material. The fastener devices are welded to at least one of the sheets of the article and the fastener devices and the sheets are made of a material having a glass transition temperature which lies between 50-60° C. and a melting point which lies between 140-180° C., preferably between 150-175° C.

FIELD OF INVENTION

The present invention relates to an absorbent article, such as a diaper,a pants-type diaper, an incontinence protector or a pants-like sanitarynapkin, said article including a front part, a rear part and anintermediate central part and also including an absorbent body which isenclosed between a liquid-permeable inner sheet or top sheet and aliquid-impermeable outer sheet or backing sheet, and fastener devices bymeans of which the side-portions of the front and rear parts can bereleasably fastened together either directly or indirectly. The fastenerdevices are located on the same side of the longitudinal symmetry lineof said article and are produced from a renewable material.

BACKGROUND OF THE INVENTION

The use of fastener devices that include mechanically coacting elementsis becoming more and more popular. Manufacturers are beginning to giveabsorbent articles a pants-like configuration. Many requirements areplaced on mechanically coacting elements of this nature. Among otherthings, they should be easy to open and close and soft enough to ensurethat a baby or other person wearing said article will not be injured bythe fastener elements. They must also be made of relatively inexpensivematerial because of the one-time use nature of the products to whichthey are attached. Such fastener devices are often made of plasticmaterial, such as polypropylene for instance, and represent anot-insignificant percentage of the material consumed in articlemanufacture when seen as a whole. It is well known that the oil fromwhich the raw material for plastic materials derives is not a renewableresource and the use of plastic materials draws on the earth's naturaloil resources. It is known from EP-A2-0 809 952 to manufacture fastenerdevices from a water-soluble or biologically degradable resin, wherewiththe fastener device has an underside which becomes adhesive upon contactwith water. Polylactic acid is mentioned as one possible material fromwhich these fastener devices can be made.

Since the use of gluing as a joining method has the drawbacks ofincurring high material costs and production complications incurred bywaste and delays in the process line, it is preferred to weld thefastener devices to the side-portions of the products. Plastic materialis thermally welded or ultrasonically welded to the outer sheets andbacking sheets normally used in the aforesaid products. However, arelatively large amount of energy is consumed in producing weld joins ofsufficient strength between outer sheets and plastic fastener devices byheat welding or ultrasonic welding processes. The maximum welding speed,i.e. the highest speed, at which a web of material can be moved past awelding unit while producing weld joins of sufficient strengthconstitutes a limiting parameter with respect to the number of productsof the aforesaid kind that can be produced per unit of time in acontinuous article manufacturing line. There is thus a need to reducethe amount of energy consumed in fastening such fastener devices, so asto achieve the advantage of enabling higher welding speeds to be used inaddition to saving energy.

The object of the present invention is to satisfy these needs and toenable the fastener devices to be made from renewable material.

SUMMARY OF THE INVENTION

These objects are achieved in accordance with the invention with anabsorbent article, such as a diaper, a pants-like diaper, anincontinence protector or a pants-like sanitary napkin, of the aforesaidkind, wherein said article is characterised in that the fastener devicesare welded to at least one of the outer sheets of said article; and inthat the outer sheet or sheets to which said fastener devices is/arefastened is/are made of a material that has a glass transitiontemperature that lies between 50-60° C. and a melting point or meltingpoint that lies between 140-180° C., preferably between 150-175° C.

In one preferred embodiment, the fastener devices and the outer sheet orsheets to which said devices is/are fastened is/are produced mainly orentirely from polylactic acid. The fastener devices each include twomutually coacting elements of which one element is fastened to the frontside-portion of the article and the other element is fastened to therear side-portion of said article and said coacting elements arefastened to either the same or to different outer sheets of saidarticle. When the coacting elements are fastened to different outersheets, both of said sheets are made of a material that has a glasstransition temperature which lies between 50-60° C. and a meltingtemperature which lies between 140-180° C., preferably between 150-175°C.

The fastener devices may be made of polylactic acid, a lactic acidcopolymer that includes caprolactone for instance, plasticized orsoftened polylactic acid or a laminate (coextrudate) that consists of acombination of these materials.

In a first variant, the fastener devices include two mechanicallycoacting fastener elements of which one element includes a part whichprojects out from the plane of said element and which can be insertedinto a recess or aperture of corresponding form in the other element,the direction of insertion being parallel to the plane of said elements.The fastener elements are fastened to the liquid-impervious outer sheet.

In another variant, each of the fastener devices includes twomechanically coacting fastener elements which each include hooked partsthat have a mutually complementary form. The fastener elements of thisvariant are fastened to different outer sheets.

In a third variant, each of the fastener devices includes twomechanically coacting fastener elements that include parts which can besnapped into each other.

In a fourth variant, the fastener devices each include two mechanicallycoacting fastener elements which include hook and loop members.

In a fifth variant, the fastener devices each include an adhesive tab.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, in which

FIG. 1 is a perspective illustration of a donned inventive diaper thatincludes fastener devices according to a first embodiment of theinvention;

FIG. 2 is a perspective illustration of one of the fastener devices onthe diaper shown in FIG. 1, and shows the fastener device in a separatedstate;

FIGS. 3A-5B are cross-sectional views of other embodiments of inventivefastener devices suitable for use with an inventive diaper;

FIG. 6 is a perspective illustration of a waist belt that can be usedmore than once and shows an absorbent unit which coacts with said beltand which includes inventive fastener devices;

FIG. 7 is a cross-sectional view taken on the line VII—VII in FIG. 6;

FIG. 8 shows a diaper provided with adhesive tabs in accordance with oneembodiment of the invention;

FIGS. 9a-h illustrate from above further embodiments of inventivefastener elements; and

FIGS. 10a-e include schematic cross-sectional views of some otherelements including the element in FIG. 9d along line X—X.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates an inventive diaper 1 donned by the wearer, wherewiththe front and rear side-portions 2, 3 have been fastened together bymeans of fastener devices 4 so as to give the diaper a pants-likeconfiguration. FIG. 1 shows only the left fastener device 4 and the leftfront and rear side-portions 2, 3 of the diaper. The diaper 1 is oftypical construction and includes an inner, liquid-permeable sheet, anouter liquid-impermeable sheet or backing sheet 16, and an absorbentbody enclosed between said inner and outer sheets, and includestypically a central part and front and rear side-portions which projectout on respective sides of said central part. A more detaileddescription of the construction of the diaper 1 is unnecessary withrespect to obtaining a better understanding of the present invention andwill not therefore be given. All of the fastener devices shown in FIGS.1-5, 9, 10 are fastened to a diaper of similar construction to thatdescribed above and corresponding components of the diaper have beenidentified with the same reference signs in said Figures.

FIG. 2 shows the fastener device 4 on the left in FIG. 1 in larger scaleand in a separated state. The device 4 includes a first element 5 whichis fastened to the front side-portion 2 of the diaper, and a secondelement 6 which is fastened to the rear side-portion 3 of the diaper 1.The first element 5 includes an inner wall 7 and an outer wall 8 whichdiverge relative to one another from one end of the first element, suchthat the walls will be mutually spaced at the other end of said element.The upper wall 8 includes a through-penetrating aperture 9. The otherelement 6 is comprised of a generally rectangular plate which includes araised surface 10 that extends generally from one end, the insertionend, slightly in towards the other end of the plate, the fastening end.The thickness of the raised surface 10 increases towards the fastenerend and the thickness of said surface at its highest part is greaterthan the greatest distance between the walls 7, 8 of the first element 5within the region of the aperture 9. The shape of the raised surface 10is complementary to the shape of the aperture 9, at least within theregion of the highest edge of said aperture. As the front end of theelement 6 (as seen in the Figures) is inserted between the walls of theelement 5 in the direction arrowed in FIG. 2, the wall 8 will be flexedoutwardly so as to allow passage of the raised surface 10. When the rearedge of the raised surface 10 (as seen in the insertion direction) haspassed the rear edge of the aperture 9 (seen in the insertiondirection), the wall 8 will spring back to its earlier position byvirtue of the elasticity of said wall, wherewith part of the raisedsurface 10 will project out through the aperture 9 beyond the wall 8such as to latch the elements 5 and 6 together.

In one variant, the raised surface 10 may include a bead or likepremonitory at least around the highest part of its upper edge, so as toeliminate the risk of inadvertently breaking the mechanical connectionbetween the elements 5 and 6. Because the side-portions strive toseparate as a result of the spring-back force, the highest part of theedge of said aperture 9 will press against the highest part of theraised surface 10 beneath the bead when the diaper is donned.

The mechanical connection between the elements S and 6 can be readilyreleased, simply by lifting the upper wall 8 to an extent such as torelease the aperture 9 from its engagement with the raised surface 10.The upper wall 8 is preferably terminated with a gripping tab 11 to thisend. When the raised surface 10 has been released from the aperture 9 inthe upper wall, the side-portions will separate as a result of saidspring-back force and the element 6 will be moved in a directionopposite to the insertion direction relative to the element 5. Thediaper is preferably provided with waist elastic in order to obtain thedesired spring-back force or re-tensioning force. Naturally, the raisedsurface 10 can be pressed down towards the lower wall 7 instead oflifting the upper wall 8, in order to move the raised surface out ofengagement with the aperture 9. The raised portion 10 is convenientlygiven a comparatively small wall thickness in order to facilitate thislatter release option.

The fastener device provided on the right side of the diaper shown inFIG. 1 is identical to the aforedescribed fastener device 4. It is, ofcourse, possible to fasten the element 6 to the front side-portion ofthe diaper instead of to its rear side-portion, as shown in the Figure,and to fasten the element 5 to the rear side-portion of the diaperinstead of to its front side-portion.

The inventive elements 5, 6 are made of a polymeric material, forinstance a material that is comprised of polylactic acid and aplasticizer or softener, such as citric acid ester. The admixture of aplasticizer or softener enhances the suppleness of the material so as toeliminate the risk of a child or other wearer being harmed by the edgeof the wall 8. The elements are preferably vacuum formed.

Polymeric material that is based on lactic acid is highly suitable as amaterial for producing fastener devices for absorbent articles of theaforesaid types. The properties of said material can be readily adaptedto the requirements placed on the special fastener devices by adjustingthe amount of plasticizer. The material may also be admixed withsubstances other than a plasticizer in order to obtain a material ofdesired properties, for instance starch. In one variant, the renewablepolymeric material may consist of a copolymer, such as a lactic acid andcaprolactone copolymer. The aforesaid polymeric material is alsosuitable for the manufacture of fastener devices, since it can bereadily vacuum formed or moulded.

When ultrasonic welding semicrystalline polymers at materialtemperatures that exceed the glass transition temperature of thematerial, the ultrasonic energy applied is absorbed as a result of thevisco-elastic energy losses (internal friction) in the material.Visco-elastic energy losses in the material are significant whenultrasonic welding thicker material, such as when welding fastenerdevices that consist of polyethylene (glass transition temperature about−120° C.) or polypropylene (glass transition temperature about −10° C.),therewith requiring the application of considerable ultrasonic energy inorder to obtain a good weld.

In the case of material where ultrasonic welding can be effected atmaterial temperatures below the glass transition temperature of thematerial, the ultrasonic energy applied is transmitted to the boundarysurface and there absorbed so as to melt the material through the mediumof external friction. The energy applied is utilised very effectivelywith such materials, since the energy is absorbed chiefly in the joinregion. In the case of polylactic acid, which has a glass transitiontemperature above room temperature (50-60° C.), the ultrasonic energyapplied is transmitted chiefly to the boundary surface, or interface,where joining shall take place. Together with the relatively low meltingpoint (140-180° C.), this is highly beneficial from a process aspect,since welding can be effected at very high web speeds. This hassignificant importance when welding together several sheets of materialand when thicker material, such as fastener devices, shall be joinedtogether.

Fastener devices that are based on polylactic acid may also beadvantageously used in heat welding processes and have been found toprovide strong welds with an energy consumption that is lower than theenergy consumed in the case of polypropylene-based material.

The low energy consumption achieved when welding fastener devices basedon polylactic acid is, of course, beneficial from an environmentalaspect. Because it is difficult generally to weld together materialsthat have mutually different melting points, the absorbent articles inwhich the fastener devices are included are also provided with at leastone outer sheet which is made of a material that has the same meltingpoint, preferably polylactic acid, wherewith the rear-side layer 16 ofthe diaper 1 is comprised of a liquid-impervious polylactic acid filmand the top-side layer is made of a nonwoven material comprised ofpolylactic acid fibres. The use of such material also provides a productthat can be handled as waste in an environmentally friendly manner.

FIGS. 3A-3C are cross-sectional views of a second embodiment of afastener device 12 that can be used on an inventive diaper 1. Similar tothe device 4 of the FIGS. 1 and 2 embodiment, the device 12 includes twoband-like fastener elements 13, 14 of which one is fastened to the frontside-portion 2 of the diaper (not shown in its entirety) and the otherelement is fastened to the rear side-portion 3 of the diaper. Thefastener elements 13, 14 consist of a fastener part 17, 18 that has anS-shape cross-section, and a rectangular part 19, 20 which forms anextension of one leg of the S-shape part and which is fastened torespective side-portions 2, 3 of the diaper. FIG. 3C shows the fastenerelements 13, 14 in an assembled state, i.e. their latching state, withthe S-shapes in mutual engagement. As will be apparent from a comparisonbetween FIGS. 3A, 3B and 3C, the S-shapes are slightly straightened outwhen inserting the parts 17 and 18 into one another. Consequently, inaddition to being shape-bound to one another when joined together intheir latching positions, the elements 13 and 14 will also be heldtogether by the spring-back force or restoring force generated as theparts 17 and 18 strive to return to their positions shown in FIGS. 3Aand 3B. The fastener element 13 is welded to the inner liquid-permeablesheet 15 whereas the fastener element 14 is welded to the outerliquid-impermeable sheet 16 of the diaper.

FIG. 4 shows a somewhat simpler variant of a fastener device 21 that canbe used with an inventive diaper 1. The fastener device 21 includesfastener elements 22, 23 that have mutually coacting fastener parts 24,25, said fastener parts having a hook-like cross-sectional shape. Inthis case, the hooked parts 22, 23 are solely shape-bound to oneanother. In order to prevent the hooks being moved vertically inrelation to one another, one of the band-like fastener elements willpreferably be broader than the other element, and the hook-part issealed at both ends. The ends of one of the band-like elements in FIGS.3A-3C are also conveniently sealed in the same way. In this embodiment,both of the elements 22, 23 are welded to the outer sheet 16 of thediaper.

FIG. 5B illustrates a third embodiment of a fastener device 26 that canbe used with an inventive diaper 1. The fastener device includes twomutually coacting, band-like fastener elements 8,7 fastened torespective side-portions 2, 3 of the front and rear parts of the diaper.The fastener elements 27, 28 each include a fastener part 31, 32 thatextends across the width of said elements and has a keyhole-shapedcross-section, as will best be seen from FIG. 5A, which shows thefastener element 28 in a load free state. The fastener parts are open attheir sides that face towards the side-portions 2, 3 of the diaper, soas to form insertion openings, and at least one of the side-portions 2,3 is slotted in the section beneath the insertion opening. The mutuallycoacting parts 31, 32 are dimensioned so that they will be held togetherby means of a snap action, subsequent to the part 31 being pressed ontothe part 32. Both of the fastener elements 27, 28 are welded to theouter sheet 16.

FIG. 6 illustrates a fourth embodiment in which mutually coactingfastener elements have been attached to a waist belt 33 and to anabsorption unit 34 respectively. In this case, the fastener devices areof the touch-and-close type 35, i.e. one of the mutually coactingfastener elements 36, 37 includes a multiple of hooked members and theother element includes a multiple of looped members. In the illustratedembodiment, the elements 37 containing hooked members are fastened tothe absorption unit, whereas the elements 36 containing the loops arefastened to the waist belt. The waist belt also includes a fastenerdevice 38 for fastening the ends of the belt together, this fastenerdevice 38 being of the touch-and-close type or some other type. Thewaist belt may be a belt that can be used several times and is made froma soft and skin-friendly material, for instance nonwoven material. Theabsorption unit 34 is comprised conventionally of an absorbent body 41enclosed between a liquid-impermeable outer sheet or backing sheet 42and a liquid-permeable inner sheet or top sheet 43, wherewith at leastthe inner sheet 43 is made of a renewable material that has a lowmelting point.

When the waist belt is made of a material that will not degradebiologically, it may be suitable to fasten the loop-bearing elements 36in a manner which enables them to be removed from the belt As will beapparent from FIG. 7, when the waist belt is made of a non-weldablematerial, the looped fastener elements 36 are fastened to the waist belt33 solely on its long-edge parts 40, for instance by gluing, andweakening lines 29, 30 are provided between said parts 40 and thecentral part of the element 36. This enables the elements 36 to beremoved from the waist belt prior to it being thrown away.

According to one advantageous variant, the waist belt 33 may be made ofa renewable material that will also degrade biologically, so that theentire belt can be treated as waste in an environmentally friendlyfashion, in which case the fastener elements 36 will not includeweakening lines.

FIG. 8 shows an all-in-one diaper which includes an absorbent body 45enclosed between a liquid-impervious backing sheet 46 and aliquid-permeable top sheet 47. The diaper also includes a front part 48,a rear part 49 and an intermediate crotch part 50. Elastic threads 51 orribbons are disposed along the edge of the rear diaper part to form awaist elastic, while elastic threads 52 are disposed along theside-edges of the diaper in the crotch part and in parts of the frontand rear parts to form leg elastic. According to the invention, twofastener tabs 53 are provided at the corners of the rear diaper part,said tabs being produced from renewable material of low melting pointthat lies between 140-180° C., preferably polylactic acid. At least therear side layer 46 of the diaper is also produced from the renewablematerial. These tabs are provided with a suitable adhesive so as toenable the side-edges of the diaper in the front and rear parts to bejoined together after the diaper has been placed on the user. If thematerial from which both the inner and outer sheets of the diaper aremade is not biologically degradable, the fastener tabs 53 may bereleasably attached to the rear-side layer in the same manner as thefastener element 37 of the FIG. 7 embodiment, for instance. This willalso apply, of course, to earlier described variants where the fastenerelements are welded to one and the same outer sheet.

FIGS. 9a-h show a number of embodiments of individual fastener elementsfrom above, said elements being usable with an inventive diaper 1. Ofthe illustrated elements, the element 54 of FIG. 9a has an ellipticalshape, the element 55 of FIG. 9b an oblong shape, the element 56 of FIG.9c a square shape, the element 57 of FIG. 9d has a recessed ellipticalshape, as will be more apparent from FIG. 10c in which the element 57 isshown in a cross-sectional view from one side. The element 58 of FIG. 9ehas the shape of a square combined with segments of a circle, and theelement 59 of FIG. 9f has a circular shape. The shape of the elementcan, of course, be varied infinitely without deviating from the basicconcept of enabling two similar elements with a small size difference tobe pressed together and therewith achieve a so-called snap-lockingeffect. In this respect, the slightly smaller so-called male element ispressed into the so-called female element, wherewith at least one ofsaid elements will comprise a material that has a given degree ofelasticity.

The female and male elements need not have precisely the same shape, butinstead may have mutually different shapes. FIG. 9g shows an example ofa male element 64 that includes recesses 66 at its respective fourcorners. This male element 64 is intended to fit into a female element65 shown adjacent the male element 64 in FIG. 9h. The female element 65lacks corresponding recesses. Without being limited to any precisetheory, it is believed that the walls defining the recesses 66 in themale element 64 can be deformed so as to facilitate insertion of themale element 64 into the female element 65.

FIGS. 10a-e illustrate further examples of fastener elements incross-section from one side. The fastener elements 57, 60-63 are shownin cross-section to illustrate the form which has a positive effect onthe latching facility afforded by the latching elements. In a preferredembodiment, the fastener elements are produced by drawing parts ofdiscrete pieces of material into air-permeable moulds by suction andtherewith form cavities, so-called vacuum forming, wherewith thematerial can also be heated to improve its shapability if necessary. Thefastener elements shown in FIGS. 9a-h and 10 a-e can either be welded toone and the same outer sheet analogously with the fastener elements 27,28 shown in FIGS. 5A, 5B, or welded to different outer sheets.

It will be understood that the invention is not restricted to thedescribed and illustrated embodiments and that these embodiments can bemodified within the scope of the invention, particularly with respect tothe design of the fastener elements of the fastener devices and alsowith respect to the material from which these devices and the outersheets are made. The invention is therefore only restricted by thecontents of the accompanying Claims.

What is claimed:
 1. An absorbent article having a front part, a rearpart and an intermediate central part, said article including anabsorbent body enclosed between an inner, liquid-permeable sheet and aliquid-impermeable outer sheet, and fastener devices for releasablyconnecting side-portions of the front and rear parts located on a sameside of a longitudinal symmetry line of said article either directly orindirectly, said fastener devices being made of a renewable material,wherein the fastener devices are fastened by welding to at least one ofthe sheets of said article; and wherein the fastener devices and said atleast one of the or sheets to which the fastener devices are fastenedare made of a material having a glass transition temperature which liesbetween 50-60° C. and a melting point which lies between 140-180° C. 2.The article according to claim 1, wherein the fastener devices and thesheet or sheets to which the fastener devices are fastened are at leastmade mainly of polylactic acid.
 3. The article according to claim 1,wherein each of the fastener devices include two mutually coactingelements of which one element is fastened to the front part side-portionof the article and the other is fastened to the rear part side-portionof said article; and wherein the mutually coacting elements are fastenedto the same sheet of said article.
 4. The article according to claim 1,wherein the fastener devices each include two mutually coacting elementsof which one element is fastened to the front side-portion of thearticle and the other is fastened to the rear side-portion of saidarticle; wherein the mutually coacting elements are fastened todifferent sheets; and wherein both sheets are made of a material thathas a glass transition temperature which lies between 50-60° C. and amelting point which lies between 140-180° C.
 5. The article according toclaim 4, wherein the melting point is between 150-175° C.
 6. The articleaccording to claim 1, wherein the fastener devices are made from one ofthe materials polylactic acid, a copolymer of lactic acid, plasticizedor softened polylactic acid or a laminate consisting of a combination ofthe aforesaid materials.
 7. The article according to claim 1, whereinthe fastener devices include two mechanically coacting fastenerelements; wherein one of said fastener elements includes a part whichprojects out from a longitudinal plane of said element and which can beinserted into an aperture or recess of corresponding shape in saidsecond element, wherein the insertion direction is parallel with saidlongitudinal plane of said element; and wherein the fastener elementsare fastened to the liquid-impermeable outer sheet.
 8. The articleaccording to claim 1, wherein each of the fastener devices includes twomechanically coacting fastener elements; wherein the fastener elementsinclude hooked parts of mutually complementary shape; and wherein thefastener elements are fastened to different sheets.
 9. The articleaccording to claim 1, wherein each of the fastener devices includes twomechanically coacting fastener elements; and wherein the fastenerelements include parts that can be snapped into one another.
 10. Thearticle according to claim 1, wherein each of the fastener devicesincludes two mechanically coacting fastener elements; and wherein thefastener elements include hook and loop members.
 11. The articleaccording to claim 1, wherein each of the fastener devices is comprisedof an adhesive fastener tab.
 12. The article according to claim 1,wherein the melting point is between 150-175° C.